بررسی تاثیر چگونگی استفاده ژئوتکستایل بر به‌سازی باربری مخلوط رس- شن در لایه‌های روسازی

هدف اصلی از این پژوهش، بررسی آزمایشگاهی تاثیر نحوۀ کاربرد ژئوتکستایل در میزان توانایی باربری خاک‌های مخلوط رسی و شنی منطقه ی باراندوز برای کاربرد در لایه‌های روسازی راه است. دراین پژوهش خاک رسی استفاده شده با خاک شنی با درصدهای (25، 50 و 75) مخلوط شده است. تاثیر ژئوتکستایل در دو حالت بررسی شد، درحالت اول به‌صورت لایه ای (یک لایه، دولایه و سه لایه در نمونه جای‌گذاری شده است) و درحالت دوم، ژئوتکستایل به‌صورت قطعاتی با ابعاد 1 ×1 و 5 ×5 سانتی‌مترمربع به‌طور تصادفی با درصد های وزنی 1، 2 و 3 درصد با مصالح مخلوط شده و رفتار مصالح ارزیابی شده است. برای انجام تحقیق از آزمون آزمایشگاهی نسبت باربری کالیفرنیا (cbr) هر دو حالت خشک و اشباع براساس استاندارد astm d1883 بهره گرفته شده است. به‌گونه‌ای که طبق استاندارد سرعت بارگذاری mm/min 1.27 انتخاب شده و عدد cbr برای نفوذ پیستون به میزان 2.5 و 5 سانتی‌متر برآورد شده است. درحالت اشباع میزان درصد تورم در نمونه ها اندازه‌ گیری شده است. نتایج حاصل از تحقیق نشان می دهد که میزان بهینۀ ژئوتکستایل مورد نیاز برای مسلح کردن مصالح بررسی شده به‌صورت قراردادن 1 لایه در قسمت میانی و یا افزودن 1% وزنی ژئوتکستایل به ابعاد1 ×1 سانتی‌مترمربع است که این میزان در شرایطی که خاک اشباع باشد به‌طور چشم‌گیری از میزان تورم می کاهد و از آن جلوگیری می‌کند.

Effects of Geotextile Applications on Bearing Capacity Clay-Gravel Mixtures in Pavement Layers

IntroductionPavement layers as a part of road structure play an important role and provide a flat and secure surface. Subgrade layer could act as a compacted embankment, natural or stabilized ground. Subgrade is a foundation of pavement layers, and it withstands all of loads due to vehicles that are transferred from upper layers (i.e., subbase, base and asphalt layers).Therefore, constructing pavements with bearing capability, high durability, quality, and maintenance in proper operating conditions is very important. However, suitable materials for constructing pavement layers are not available, and improvement techniques should be employed for them. Generally, different methods such as mechanical or chemical are available for improvement. Nowadays, geosynthetic materials such as geotextile and geogrid are used to optimize and enhance the bearing capacity of pavement layers. The present study is aimed to investigate the effects of geotextile applications on bearing capacity of claygravel mixtures in pavement layers.Material and MethodsIn this research, materials were prepared from Barandouz area. Clayey soil was mixed with gravel in 25, 50 and 75 percentages (by weight). Geotextile was woven and made of polypropylene (with commercial name FibertexF32). Geotextile effects in mixture were evaluated in two conditions. Position number one indicates the arrangement of geotextile. This means, at first, one geotextile layer was embedded in the middle of materials. Then, two and three geotextile layers in equal depths from each other were used in soil mixtures. Position number two shows the mixing pieces randomly. This means that geotextile pieces in 1 ×1 and 5 ×5 cm2 were prepared and were randomly mixed with materials in 1, 2 and 3 percentages (by weight). For evaluating geotechnical behavior of improved claygravel mixtures, compaction and California bearing ratio test (CBR) (in dry and saturate conditions) based on ASTM were performed. It should be noted CBR test in dry and saturate conditions were carried out in three different compaction energies (i.e. 10, 25 and 56 blow count for per layer). Moreover, CBR was evaluated for piston penetration at 2.5 and 5 cm in the specimen.Results and discussionThe findings of this study could be summarized as:1. Results of compaction test showed that, in the unimproved position, with increasing gravel content in clay, maximum dry unit weight ( gamma;dmax) has been increased, while simultaneous optimum water content (wopt) decreased.In the improved position, in the first mode, when a geotextile layer was embedded in the middle of the specimens, gamma;dmax reached to its upper value, whereas wopt reached to its minimum value. On the other hand, with an increase in the number of geotextile layers in claygravel mixtures, dry density has been decreased, but optimum water content increased. Furthermore, in the second mode, when geotextile pieces with 1 ×1 and 5 ×5 cm2 were randomly mixed in the specimens, the findings revealed that geotextile pieces with 1 cm2 areas and 1% by weight in claygravel mixtures increases gamma;dmax and reduces wopt.2. In dry and saturate conditions, California bearing ratio (CBR) test result displayed that in the unimproved condition, with an increase in gravel content in the clay, CBR value has been increased. In the improved situation, in the first mode, when a geotextile layer was embedded in the samples, CBR had a maximum value in all of the compaction energies even though it is reduced as the number of layers increased. In the second mode, when geotextile pieces in 1 ×1 cm dimensions with 1% (by weight) were randomly mixed with the specimens, CBR value reached at high. In contrast, with increasing dimensions of pieces and percentages in the presence of geotextile in claygravel mixtures, CBR values declined. Therefore, it can be concluded that, according to Code 234 (Iran Highway Asphalt Paving Code), the application of one geotextile sheet in the middle of materials or geotextile pieces in 1 ×1 cm dimensions with 1% (by weight) random mixing is suitable for subbase and base layers in pavement design.3. CBR test results in the saturate condition in claygravel mixtures illustrated that, in the nonreinforced condition, with an increase in clay content in specimens, swelling value keeps rising sharply. On the contrary, in the reinforced position with embedding a geotextile layer in the middle sector of samples or through adding geotextile pieces (1 cm2) with 1 % content (by weight) to the specimens, the rate of swelling significantly decreased. ConclusionTo sum up, the main objective of the present study was to investigate the impact of geotextile applications on bearing capacity of claygravel mixtures in pavement layers. The findings demonstrated that when geotextile as a layer was embedded in the middle part of specimens or as pieces with 1 ×1 cm dimensions and 1% content (by weight) was randomly mixed with the mid materials, the bearing capacity of the reinforced specimens was enhanced. In contrast, in the saturate condition, swelling potential significantly was reduced. It is noteworthy to mention that 1 cm2 pieces of geotextile is more effective than the layers. This is due to the fact these pieces make aggregates closer to each other. Thereby, minimum void ratio (emin) reaches its least value, the structure of grading improves, and the contacts between particles and geotextile pieces rise. As a suggestion for further research, it looks promising to evaluate the dynamic properties and the behavior of the improved materials with other geosyntheticses.